Do they make jeans like this?

I'm a freshman guy and I know absolutely nothing about clothes. My gf has been working out a lot the last few months and one of the ways it's been showing the most is in the shape of her ass. I was thinking of buying her a pair of jeans to accentuate this for valentine's day, but here's my problem: She doesn't like all tight jeans, so they would have to be tight around the butt and then looser on her thighs and calves. Do they make jeans like this, and if so, where could I get a pair that's not horrendously expensive?